Pollution Risks Of Heavy Metals In Irrigated Water On Soils And Crops

With the rapid development of economy, some areas of China have been shortage of water because of water pollution such as rich nutrient and so on. The problem of shortage of water resources has also been exacerbated. Wastewater irrigation could alleviate the conflict of water providing and demanding on some degree. But part of civil and industry wastewater always contains heavy metals or organic compounds. Using wastewater irrigation it may lead to poisonous pollutants accumulated in soils and crops. Beijing is a super scale city which has long history and the history of wastewater irrigation is also fairly long. Until recently, however, the research of the accumulation of heavy metals in large irrigated areas is not systematic and whole. Recently, with perfecting of environmental protection measure and improving of environmental technology, the heavy metal level in wastewater has clearly changed. So it is still a key research on the dynamic effects of wastewater irrigation on the whole irrigation area environment. At present, Beijing and some lack-water cities plan to develop large scale recycle of post-treatment sewage, so the deeper research of effects of wastewater irrigation on heavy metal accumulation also has consulting value for evaluating environmental risks in recycle of post-treatment sewage.The study selected a typical wastewater-irrigated area - southwest Liangshui river and Fenggang river of Tongzhou, Beijing. We conducted the systemic research on the accumulation of heavy metal in wastewater-irrigated area. Take the typical wastewater-irrigated area as an example, we investigated the heavy metal accumulation in soils and crops systemicly. Discussing the status in quo of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn pollution and the origin and path of pollutants, through the model of soil column combining the field investigation of soil profile, we evaluate the polluted risks of heavy metal on the low underground water and reasonably evaluate the effects of wastewater irrigation on ecological environment of Liangfeng irrigated area of Tongzhou.1. Through the investigations of heavy metals in surface soil (0-20cm) of Liangfeng irrigated area of Tongzhou, Beijing, we determined the soil pollution of Hg was more serious, Cu and Pb pollution was secondary, As, Cr and Zn pollution was little. Compared with the investigations in 1975, the concentrations of Hg, Pb and Cu had increased by 11.36%, 40% and 26%, respectively. The concentration of Hg had an affinity for wastewater irrigation, meanwhile, restricted by other factors such as soil character and so on.2. On the basis of primary analysis on heavy metal concentrations of surface soil, we analyzed the spatial relativity of pollutants and described the spatial model of soil character using half-variation function. Then through kriging analysis, we analyzed the spatial-distributingcharacter of heavy metals in irrigated area and confirmed the pollution sources and provided bases for farther preventing soil pollution and reasonable wastewater irrigation. The research which analyzed the spatial structure of concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn using statistic method in the soil of Liangfeng irrigated area indicated that the 8 kinds heavy metals all show well transition character. The semivariogram of As, Cd, Cr, Cu, Hg could be fitted well with global model and Ni, Pb, Zn could be fitted well with exponential model. The high concentration of Hg mainly concentrated in the area of Liangshui river and the high concentrations of As, Cu, Hg and Pb also had distribution in it Relative to Liangshui river, the content of As, Cr, Hg, Pb and Zn was lower, but the content of Hg, Cu and Pb exceeded the soil baseline in different degree in large area, behaving higher pollution risks. In irrigated soils, the source of Hg mainly is wastewater irrigation and a part of Cd* Cr and Pb also comes from it As, Ni and partly Cr mainly affected by soil character, the sources of Cu and Zn have diversity.3. The heavy metals presented definite pollution in soils of Liangfeng irrigated area, we investigated the concentrations of heavy metals in crops growing on Liangfeng irrigated area. Take wheat as an example, we analyzed concentrations of 8 kinds heavy metals in wheat seeds and determined that there were distinct heavy metal pollution in them. The percent superscales of Ni, Pb and Zn were 38.1%, 28.6% and 4.8%, respectively, meanwhile, in some samples, the concentrations of Hg and Cd were close to the standard of Chinese food hygienic standards. Compared with the results of investigation in 1976, the concentrations of Hg, Pb and Cu had significant increase in wheat seeds and the pollution of these heavy metals showed aggravating trend. The wheat seeds had strong accumulating ability of Zn, Cu and Cd, the secondary was Hg, Pb and Ni, the last was As and Cr. The validity coefficient in soil and the accumulating coefficient in wheat seeds of Cd and Hg were distinct relative.4. Through the soil column model in lab, taking As, Cd , Cu and Pb as examples and leaching the soil column at different quantity of irrigation and different condition of water quality, we found that As, Cu and Pb mainly concentrated in depth of 0-50cm and had little trend to move to deep soil and had little risk to low underground water; Cd had strong trend to move to deep soil and had definite risk to low underground water of 1 m; when the concentration of extraneous pollutants were lower, the distribution of them was comparatively even; when higher, the pollutants accumulated in the surface soil and the content was clearly higher than...